Molecules& Compounds
When molecules connect with molecules , _____________ are created.
molecular compounds
How many elements are found so far?
118
Chemical changes are __________ (impossible to bring back).
Irreversible
Atoms, elements, and compounds play a ___________ role in our daily life.
crucial
___________ are the building blocks of all matter.
Atoms
N2 and O2 are examples of ____________ because they consist of 2 atoms as molecular compounds.
diatomic molecules
Atoms of the same element that have a different number of neutrons are called _____________.
isotopes
Chemical changes follow a principle called ___________. It means matter can not be created or destroyed and the mass stays unchanged.
conservation of mass
Mixtures can be separated by _________ methods while compound can be separated by ____________ methods.
physical; chemical
Protons carry a __________ charge and neutrons have ___________ charge. However, electrons carry ___________ charge.
positive; no; negative
What are electron shells?
the places surrounding the nucleus of an atom where electrons are found
What is the composition of elements in the periodic table?
metals, non-metals and metalloids
What is the nature of chemical changes?
Chemical changes involve breaking and forming atomic bonds , leading to the formation of new compounds.
Compounds have fixed ___________ and new ____________.
ratio; property
What is the composition of an atom?
At the center lies the atomic nucleus which contains protons and neutrons. Also, electrons surround the nucleus.
What are valence electrons?
electrons found in the outermost shell
Please introduce the properties of the alkali metals, alkaline earth metals, the halogens and the noble gases.
Alkali metals- Group 1-very reactive metals
Alkaline earth metals- Group 2- a little reactive
Halogens- Group 17- reactive non-metals
Noble Gases- Group 18- very unreactive
Give 2 examples of atoms which have some certain physical properties.
Iron-reactivity
Hydrogen-flammability
What is the difference between elements and compounds?
Atoms of the same type bond together to form elements but atoms of different types of atoms bond together through chemical reactions, they form compounds.
A neutral atom has an equal number of ________ and _____________. An atom loses 1 electron to from a _____________.
protons; neutrons; ion
分子化合物，双原子分子，电子层，化学键，最外电子层，最外层电子
molecular compound, diatomic molecule, electron shell, chemical bond, valence shell, valence electrons
原子序数 族 周期 同位素 中性元素 化学符号 平均原子质量
atomic number, family (group), period, isotope, neutral element, chemical symbol, average atomic mass
延展性 溶解性 可燃性 反应性 硬度 物理属性
malleability; solubility; flammability; reactivity, hardness, physical property
物质 原子 元素 化学反应 化合物 混合物 分子
matter atom element chemical reaction compound mixture molecule
颗粒
原子核
质子
中子
原子质量单位
particle
nucleus
proton
neutron
atomic mass unit (amu)